An Organic Light-Emitting Diode (OLED) is also known as an Organic Electroluminesence Display (OELD). The OLED, with self-luminous property, has a very thin organic-material coating and a glass substrate; when electrical current passes through, the organic material will emit light; moreover, an OLED display screen has a large viewing angle, and can significantly save electrical energy, so the OLED screen has many advantages unparalleled by a liquid crystal display (LCD).
Generally, light of an OLED device is always emitted from a lower substrate, that is, bottom emission. And so-called top emission refers to that light does not pass through the lower substrate, but exit from an upper side which is opposite thereto. If on the substrate, there is a highly-reflective first electrode, and a second electrode is light-transmissive, then light exit from the exterior second electrode. If the first electrode is made of a conventional light-transmissive ITO in combination with the light-transmissive second electrode, then both sides of the device will emit light.